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What Is Preterm Labor and Birth?

Contractions and dilation (opening) of the cervix before 37 weeks of pregnancy is considered preterm, or premature, labor. A normal pregnancy lasts about 40 weeks after the first day of the last period (38 weeks after fertilization). The danger of preterm labor is that it will lead to the birth of a baby that has not fully developed, and therefore has a high risk of problems. About 10% of all pregnancies result in premature birth. The majority of serious complications or infant deaths are due to consequences of premature birth.

Preterm labor can be extremely frightening, because parents-to-be quite naturally fear that their baby will be born too early and suffer the problems of prematurity. If your baby is born too soon, there is a great chance that her lungs will be underdeveloped. If so, she'll need to be put onto a ventilator that can breathe for her. Receiving oxygen through a ventilator can lead to complications, so doctors try to get premature infants off the ventilator as soon as possible.

Your baby may also have trouble maintaining a normal body temperature, and may become hypothermic (too cold). She'll need to be kept warm. Your baby might be so early that she can't coordinate her muscles to suck and swallow. If this is the case, she'll have to be fed through a needle in the vein (intravenously), or through a tube passed into her nose, down her throat and into her stomach. A premature baby may also develop complications such as bleeding into the brain; an increased risk of infections, especially meningitis and sepsis (serious bloodstream infection); problems with kidney function; and jaundice.

Premature babies are at higher risk for long-term complications, which may include vision impairment or blindness, hearing impairment, cerebral palsy, and chronic lung problems. The earlier the baby is born, the more likely that she will have these problems.

You are more likely to experience preterm labor if:

• You have had preterm labor or delivered a premature infant in the past.
• You are carrying more than one baby (such as twins or triplets).
• Your mother used the medication diethylstilbestrol (DES) while she was pregnant with you.
• You have an abnormally shaped uterus or an abnormal cervix.
• You have had a cone biopsy of your cervix in the past.
• You are younger than 17 or older than 35 years.
• You belong to a non-white race.
• You are living in poverty.
• You got pregnant while using an IUD, and it is left in place during the pregnancy.
• You were seriously underweight when you became pregnant.
• You smoke or use cocaine or other street drugs.
• You have had second-trimester miscarriages during previous pregnancies, or you have had three or more elective abortions.
• You are not receiving prenatal care from a qualified health-care provider.
• You have a cervical infection, such as group B streptococci, gonorrhea, chlamydia, syphilis, "trichomoniasis", or gardnerella.
• Your job entails doing extremely physical and strenuous work.

What Causes It?

Premature delivery may be preceded either by contractions or premature rupture of the fetal membranes (PROM), when the water breaks before labor begins.

Although there have been many advances in caring for premature babies, there has been no improvement in solving the problem of preterm labor or PROM. We don't completely understand why some women go into labor or break their water too early. We are often unable to accurately predict which women will do so, and we are limited in preventing these women from giving birth prematurely.

In some cases, an infection may be involved; in others, it may be an abnormally short cervix or a combination of factors. In about half of all cases, no cause can be found. The number of babies born prematurely in the U.S. has actually risen in recent history.